One hour after onset of ischemia, 5-HT level was significantly increased in ischemic hemispheres, and was not further changed up to 6 hours duration of ischemia. The levels of DA and NOR were reduced 1 hour after the occlusion was established and the reduction of these concentrations were proportional to the duration of ischemia. In recovery after ischemia, one hour and 15 minute occlusion, as well as 1 hour after 1 hour occlusion, 5-HT level was significantly higher than it was during ischemia, while in gerbils which were ischemic for longer periods, 5-HT levels were significantly lower than in ischemia. Twenty hours after the clip was removed, 5-HT level in animals which were ischemic for 15 minutes reached the peak and was higher than 1 hour after the clip was removed in the same experimental group of animals. The behavior of DA and NOR was in agreement with the principles of the "maturation phenomenon", i.e., the lowest depressions of these catecholamines were observed at 20 hour post-ischemic period following 15 minute occlusion and at 5 hours after release following 1 hour ischemia.